1. Field of the Invention
This invention relates to an apparatus and method for estimating the binary error rate for a binary coded input data stream associated with a digital receiver (binary receiver). Such a receiver is employed in, e.g., satellite communication systems and in earth monitoring stations therefor.
2. Description of the Prior Art
Certain prior methods have been used to detect errors on digital signals. For example, U.S. Pat. No. 3,757,296 describes an error detection system for detecting actual errors in a partial response transmission system wherein separate level detectors are provided for positive and negative pulses so that when the magnitude of the signal voltage exceeds a predetermined maximum in either direction, an error signal is produced.
U.S. Pat. No. 3,248,695 discloses a binary signal error detection system in which in one embodiment error indication is provided each time a pulse amplitude is less than one-half of the signal data input or greater than twice the value of the signal voltage. The error detection system of this patent operates on a data stream having code characters of the parity check type.
U.S. Pat. No. 3,825,892 discloses an error detection system for a low disparity binary code (number of MARKS and SPACES is approximately equal) in which the low frequency component of the average signal value is an indication of signal error.
U.S. Pat. No. 3,721,959 teaches a system in which the error is defined as a forbidden window within an eye pattern with reference voltage height and reference time width.
U.S. Pat. Nos. 3,204,189 and 3,214,700 also disclose error detection systems.
None of the prior art estimates the BER by just measuring an event which is more than twice the amplitude and of the same polarity with respect to the normal signal voltage.
What is needed is a simple, accurate and economical circuit for estimating the bit error rate which functions independently of any particular bit pattern, which can be used for on-line monitoring without decreasing the information carrying capabilitiy of the link (e.g., the use of parity bits decreases said capability) and which accumulates a statistically significant sample in the same time as that required for a direct comparison between sent and received bits. These requirements are met by the present invention.